Biocrystal-encased manganese ferrite (BC@MnFe 2 O 4 ), an adsorption/catalytic bifunctional catalyst, was synthesized for peroxydisulfate (PDS) activation and tetracycline (TC) removal. Under the optimal conditions (PDS 6.0 mM, pH 7.0, dosage 0.30 g L −1 , and TC content 20.0 mg L −1 ), the TC removal efficiency reached 85.11% and maintained 79.07% after four cycles. Furthermore, inorganic anions (H 2 PO 4 − > HCO 3 − > NO 3 − > SO 4 2− > Cl − ) and natural organic matter (HA) inhibited TC elimination to varying degrees. Compared with the MnFe 2 O 4 nanorods, BC@MnFe 2 O 4 effectively alleviated the side effects caused by particle aggregation and reduced metal ion leaching. Adsorption kinetic and isotherm results exhibited that the adsorption process of TC on MnFe 2 O 4 and BC@MnFe 2 O 4 were better fitted with the pseudo-second-order and Langmuir models. The analyses of quenching experiment, electron paramagnetic resonance, and X-ray photoelectron spectroscopy demonstrated that Fe and Mn sites exposed on the BC@MnFe 2 O 4 served as the catalytic centers for PDS activation, and OH, SO 4 − , and 1 O 2 were crucial reactive oxidant species contributing to the rapid TC degradation. Based on the determination of TC degradation intermediates, three possible degradation pathways were proposed, and TC was converted to small molecules via hydroxylation, demethylation, deamidation, dehydration, and other reactions. This study offers novel insights into the synergistic effect of adsorption and catalysis by inorganic-biological hybrid design, and gives inspiration for the construction of high-performance catalysts in organic wastewater treatment.
Silicon (Si) has been proven to significantly enhance CO 2 reduction efficiency of numerous catalysts. However, the lack of research on Si's effect on manganese ferrite catalytic performance presents a challenge in using high-silica manganese ore to prepare cost-effective, efficient manganese-based ferrite decarbonization catalysts. This work prepared Nano-MnFe 2 O 4 materials containing 0.0%–9.3%Si (2.3% increments, in mass fraction) by solid-phase synthesis (1300 °C, air) and nano-grinding. The effect, mechanism, and enhancement strategy of Si on the low-temperature catalytic reduction of CO 2 to carbon (C) performance of Nano-MnFe 2 O 4 were systematically investigated. Results showed that introducing Si transformed Nano-MnFe 2 O 4 into Nano-Mn X Fe 3– X O 4 (0.75 < X < 1.00) with degraded catalysis and Nano-Fe Y Mn Z SiO 4 with almost no activity, lowering CO 2 reduction to C from 5.55 mmol/g to 2.81 mmol/g. Increasing Si concentration simultaneously decreased the content and X -value of Nano-Mn X Fe 3- X O 4 , causing fewer oxygen vacancies and declined CO 2 reduction. A phase reconstruction strategy to eliminate Si impact and enhance catalysis was proposed, i.e. , adding MgO, increasing Mn/Fe ratio, and nano-grinding followed by magnetic separation. Nano-Mg 0.19 Mn 1.70 Fe 1.11 O 4 reconstructed from Nano-MnFe 2 O 4 with 2.3% Si exhibited 8.82 mmol/g CO 2 reduction and 100% carbon conversion at 350 °C. Mg 2+ doping strengthened the conversion of Mn 2+ to highly catalytically active Mn 3+ and Mn 4+ ions, increasing oxygen vacancies and electron transport for C=O rupture.
Hao Wang,Wenxin Bao,Muhammad Tariq Sarwar,Luyuan Tian,Aidong Tang,Huaming Yang
Local geometric configurations of metal cations in inorganic enzyme mimics determine their catalytic behaviors, while their optimization remains challenging. Herein, kaolinite, a naturally layered clay mineral, achieves the optimization of cationic geometric configuration in manganese ferrite. We demonstrate that the exfoliated kaolinite induces the formation of defective manganese ferrite and makes more iron cations fill into the octahedral sites, significantly enhancing the multiple enzyme-mimicking activities. The steady-state kinetic assay results show that the catalytic constant of composites toward 3,3′,5,5′-tetramethylbenzidine (TMB) and H2O2 are more than 7.4- and 5.7-fold higher than manganese ferrite, respectively. Furthermore, density functional theory (DFT) calculations reveal that the outstanding enzyme-mimicking activity of composites is attributed to the optimized iron cation geometry configuration, which has a higher affinity and activation ability toward H2O2 and lowers the energy barrier of key intermediate formation. As a proof of concept, the novel structure with multiple enzyme-mimicking activities amplifies the colorimetric signal, realizing the ultrasensitive visual detection of disease marker acid phosphatase (ACP), with a detection limit of 0.25 mU/mL. Our findings provide a novel strategy for the rational design of enzyme mimics and an in-depth investigation of their enzyme-mimicking properties.
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